Copper‐catalyzed reactions: Research in the gas phase

Trifluoromethylation reactions have recently received increased attention because of the beneficial effect of the trifluoromethyl group on the pharmacological properties of numerous substances. A common method to introduce the trifluoromethyl group employs the Ruppert-Prakash reagent, that is, Si(CH3 )3 CF3 , together with a copper(I) halide. We have applied this method to the trifluoromethylation of aromatic alkynes and used electrospray-ionization mass spectrometry to investigate the mechanism of these reactions in tetrahydrofuran, dichloromethane, and acetonitrile as well as with and without added 1,10-phenanthroline. In the absence of the alkyne component, the homoleptic ate complexes [Cu(CF3 )2 ](-) and [Cu(CF3 )4 ](-) were observed. In the presence of the alkynes RH, the heteroleptic complexes [Cu(CF3 )3 R](-) were detected as well. Upon gas-phase fragmentation, these key intermediates released the cross-coupling products R-CF3 with perfect selectivity. Apparently, the [Cu(CF3 )3 R](-) complexes did not originate from homoleptic cuprate anions, but from unobservable neutral precursors. The present results moreover point to the involvement of oxygen as the oxidizing agent.

Section: Introductionmentioning

confidence: 99%

The Role of Ate Complexes in the Copper‐Mediated Trifluoromethylation of Alkynes

Weske

Schoop

Koszinowski

2016

“…To shed more light on these problems, we here turn to electrospray ionization (ESI) mass spectrometry, which can provide information on organocuprates complementary to that obtained by NMR spectroscopy by selectively probing the charged species present in solution. Previous work has shown that this method is well‐suited to detect and characterize even highly reactive organocopper ions . Gas‐phase experiments on mass‐selected organocopper ions, moreover, make it possible to probe their intrinsic reactivity in unprecedented detail and without any interference from dynamic equilibria, which severely complicate their analysis in solution …”

Section: Introductionmentioning

confidence: 99%

“…Previous work has shown that this method is well‐suited to detect and characterize even highly reactive organocopper ions . Gas‐phase experiments on mass‐selected organocopper ions, moreover, make it possible to probe their intrinsic reactivity in unprecedented detail and without any interference from dynamic equilibria, which severely complicate their analysis in solution …”

Section: Introductionmentioning

confidence: 99%

“…Previous work has shown that this methodi sw ell-suited to detect and characterizee ven highly reactive organocopper ions. [18][19][20] Gasphase experimentsonmass-selected organocopper ions, moreover,m akei tp ossible to probe their intrinsic reactivity in unprecedented detail and without any interference from dynamic equilibria, [19][20][21] which severely complicate their analysis in solution. [22] As the addition of organocuprates to a,b-unsaturatedc arbonyl compounds proceeds too fast to interceptt he involved intermediates by ESI mass spectrometry,w ee mployedt he less reactive a,b-unsaturated cyanoethylenes (C 2 H 4Àn (CN) n , n = 1-4; Figure 1) as Michael acceptors.…”

Section: Introductionmentioning

confidence: 99%

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Intermediates Formed in the Reactions of Organocuprates with α,β‐Unsaturated Nitriles

Putau

Brand

Koszinowski

2016

Conjugate additions of organocuprates are of outstanding importance for organic synthesis. To improve our mechanistic understanding of these reactions, we have used electrospray ionization mass spectrometry for the identification of the ionic intermediates formed upon the treatment of LiCuR2 ⋅LiCN (R=Me, Bu, Ph) with a series of α,β-unsaturated nitriles. Acrylonitrile, the weakest Michael acceptor included, did not afford any detectable intermediates. Fumaronitrile (FN) yielded adducts of the type Lin-1 Cun R2n (FN)n (-) , n=1-3. When subjected to fragmentation in the gas phase, these adducts were not converted into the conjugate addition products, but re-dissociated into the reactants. In contrast, the reaction with 1,1-dicyanoethylene furnished the products of the conjugate addition without any observable intermediates. Tri- and tetracyanoethylene proved to be quite reactive as well. The presence of several cyano groups in these substrates opened up reaction pathways different from simple conjugate additions, however, and led to dimerization and substitution reactions. Moreover, the gas-phase fragmentation behavior of the species formed from these substrates indicated the occurrence of single-electron transfer processes. Additional quantum-chemical calculations provided insight into the structures and stabilities of the observed intermediates and their consecutive reactions.

“…[8] In addition to these gas-phase ion/molecule reactions, there also exist alarge number of studies dealing with gas-phase isomerization of Cu complexes. [9] However, regarding the thermal activation of methane in the gas phase by copper-containings pecies, there are only af ew studies:d iatomic [CuO] + brings about both Ha tom and O atom transfers in itsr eactions with methane; [10] in addition, a mechanistically unique concerted insertion of ac arbon atom into two CÀHb onds of methane to generate [Cu(C 2 H 4 )] + has been reported for the [CuC] + /CH 4 system. [11] ½Al 2 CuO 5 þ þ CH 4 !½Cu þ þ ''Al 2 O 5 CH 4 '' ð1Þ…”

mentioning

confidence: 99%

Selective C−O Coupling Hidden in the Thermal Reaction of [Al₂CuO₅]⁺ with Methane

Zhou

Sun

Yue

et al. 2018

The thermal gas-phase reaction of [Al CuO ] with methane has been explored by using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. The generation of atomic [Cu] from the [Al CuO ] /CH couple corresponds to the only reaction channel. Labeling experiments and computational studies strongly suggest that methane activation is indeed involved in the production of [Cu] , and generation of CH O prevails. Mechanistic aspects and the associated doping effects are discussed.